This proposal centers around studies of the retina as a model system of a neural tissue and as a system for the study of biochemical control mechanisms in this tissue. The major focus is on glutamine synthetase (GS) and other enzymes that may be related to the visual function of the retina, as well as on general retinal metabolism. GS, which is present in high concentrations in the neural retina, can be prematurely induced in embryonic chick retina by glucocorticoids, e.g. cortisol. The role of cell-cell interactions in the inductive process is being studied, as are the inhibitory and enhancing effects on the induction by glutamate, some glutamate analogs, and other related compounds. L-glutamate severely damages embryonic and neonatal retina both in vivo and in culture. We have shown that the initial effects of glutamate are to the Muller cells of the retina. We have also localized GS activity to these cells. The main emphasis of the current and future work is to attempt to elucidate further the biochemical and morphological effects of glutamate, glutamate analogs, and related compounds on retinal tissue. We plan to study the effects of time and concentration of treatment on the magnitude of the observed effects. The age dependence of these parameters is also under study. The investigations are geared toward elaboration of a mechanism of action of glutamate within retinal tissue.